Zinc Oxide UV Filter Particles for Photostable Color Control
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Solution Overview
Problem
Zinc oxide particles used in UV filters and cosmetics develop an undesirable yellow coloration due to oxygen vacancies and photocatalytic activity, which is not acceptable for commercial use, and existing methods to prevent this are impractical for small particles required in UV filters.
Innovation Solution
Developing stoichiometric zinc oxide particles with a specific O:Zn ratio, average particle size of 10 to 300 nm, and controlled defects to quench excitons, combined with optional coatings to enhance photostability and cosmetic compatibility, while maintaining a non-pigmentary size to avoid visible light scattering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If zinc oxide particles are used as UV filters with small particle size (300 nm or less), then light scattering is avoided and UV filter performance is improved, but the particles develop yellow coloration due to oxygen vacancies which is commercially unacceptable
Solution Approach 1:
The patent changes the chemical composition parameters by controlling the O:Zn ratio to be within 0.97-1.03 and limiting dopant concentrations to very low levels (Al: 0.01-0.1%, Si: 0.01-0.1%). This precise parameter control prevents excessive oxygen vacancies while maintaining UV filter effectiveness, resolving the contradiction between small particle size performance and color stability.
Solution Approach 2:
The patent applies localized surface treatments with specific coatings (silica, alumina, titanium dioxide, or organic coatings) that selectively modify the particle surface properties without affecting the bulk UV filter performance. This local modification approach prevents coloration at the surface level while maintaining the small particle size benefits for UV protection.
2Object-generated harmful factors
If doping with oxygen-rich oxides is used to prevent oxygen vacancy formation and maintain white color, then pigmentary particle color stability is improved, but the method is not practical for UV filter particles due to severe purity requirements and limited dopant amounts
Solution Approach 1:
The patent establishes specific compositional parameters (O:Zn ratio of 0.97-1.03, very low dopant levels) that are practical for UV filter particle manufacturing while still achieving color stability. This differs from traditional pigment doping by using minimal dopant amounts that meet purity requirements without compromising UV filter performance.
Solution Approach 2:
The patent uses surface coatings as intermediary layers that prevent oxygen vacancy formation and maintain color stability without requiring bulk doping. The coatings act as mediators between the zinc oxide particles and the environment, providing color stability while maintaining the purity and performance requirements for UV filter particles.
3Length of moving object
If mechanical grinding is applied to zinc oxide particles, then particle size is reduced for UV filter application, but oxygen vacancies are created which cause yellow coloration
Solution Approach 1:
The patent performs preliminary oxidation treatment or surface coating before the particles are used in formulations. This preliminary action prevents oxygen vacancy formation during subsequent mechanical processing or application, allowing particle size reduction through grinding without creating harmful coloration.
Solution Approach 2:
The patent introduces surface coatings as intermediary protective layers that prevent mechanical damage and oxygen vacancy formation during grinding. These coatings mediate between the mechanical processing required for UV filter application and the need to prevent coloration, allowing size reduction without compromising color stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution results in photocatalytically stable, photostable zinc oxide particles that maintain a commercially acceptable orange to tan color, reducing photocatalytic activity and improving aesthetic and functional properties in cosmetic formulations.
Implementation Method 1
Zinc oxide particles both absorb and scatter UV radiation, with the former playing a larger role as particle size decreases. The absorption of UV radiation in inorganic UV filters including zinc oxide results in the formation of electron-hole pairs known as excitons.
Implementation Method 2
Pigmentary particles typically have larger sizes (from greater than 300 nm to about 16 mm) in order to scatter visible light, while particles used in UV filters typically have small particle sizes (300 nm or less) in order to avoid scattering light.
Implementation Method 3
Defects may be introduced into zinc oxide to quench excitons. The introduction of traps serves the purpose of trapping electrons and holes created upon excitation of the zinc oxide particles with UV radiation.
Implementation Method 4
Such reactions may be impeded by sequestering the charge carriers created from UV absorption through targeted surface treatments or through quenching of the exciton species.
Data Source
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AI summary
Zinc oxide particles are prepared as a dry powder through a vapor phase formed by a plasma process, or by introducing defects into stoichiometric zinc oxide particles in a liquid carrier through mechanical stress. The zinc oxide has an O:Zn ratio of at least 0.99, an average particle size of 10 to 300 nm, and a sufficient concentration of oxygen vacancies and zinc vacancies to give a dispersion of the particles in C12-C15 alkyl benzoate an orange to tan color corresponding to a ΔE value of at least 15 in a Dispersion Color Test. The particles contain no aggregates and have no detectable particles 500 nm or larger, on a number-weighted basis